The long-range goal of this project is to elucidate structure- function relationships for electron transfer reactions involving both soluble and membrane-bound redox proteins. Reactions of this type are the basis for some of the most important and fundamental processes in biology, including respiration and nitrogen fixation, and are a part of virtually all metabolic systems. Electron transfer has also been implicated in oncology, toxicology and the aging process. Out approach utilizes fast kinetic techniques (stopped-flow spectrophotometry and laser flash photolysis) as a probe of the steric and electrostatic properties of the electron transfer site in a wide variety of systems which have flavin, heme, iron-sulfur and copper redox centers. Specific goals involve the study of electron transfer between two protein moieties in solution, in electrostatically- stabilized 1:1 complexes, in multi-subunit proteins and in protein- lipid bilayer assemblies. Some of the systems to be studied are the flavodoxin-cytochrome c, the cytochrome c-cytochrome peroxidase and the ferredoxin-ferredoxin reductase complexes, flavocytochromes such as p-cresol methylhydroxylase, trimethylamine dehydrogenase (an iron-sulfur flavoprotein), bacterial photosynthetic reaction centers, the cytochrome P450 system and the cytochrome c-cytochrome oxidase system.